A pseudo type data type in PostgreSQL is a special data type that does not have a corresponding storage format. It is used to define the behavior or characteristics of a column or a function’s return value, without actually storing any data.
What are Pseudo Types?
Pseudo types in PostgreSQL are used to represent various types of values that do not fit into the traditional category of data types. They are typically used for input and output purposes, rather than for storing actual data.
Commonly Used Pseudo Types in PostgreSQL:
- anyelement: This pseudo type can be used as a parameter or return type of a function to indicate that it can accept or return any data type.
- anyarray: This pseudo type represents an array of any dimension and can be used as a parameter or return type when dealing with arrays.
- anynonarray: Similar to anyarray, this pseudo type represents any non-array data type.
- void: The void pseudo type indicates that a function does not return anything.
- trigger: This pseudo type is used to define trigger functions and represents the row-level change made to a table.
The Usage of Pseudo Types
Pseudo types are primarily used in functions and triggers to provide flexibility and genericity. By utilizing these types, developers can create functions that work with different data types without having to write separate functions for each specific case.
For example, let’s consider a scenario where we need to create a function that accepts an array as input and returns the sum of all elements in the array. Instead of creating separate functions for each possible array data type such as integer, text, or numeric, we can use the anyarray pseudo type as the parameter type. This allows us to handle arrays of any data type in a single function.
Here’s an example of a function that calculates the sum of an array using the anyarray pseudo type:
CREATE FUNCTION array_sum(arr anyarray) RETURNS numeric AS $$ DECLARE total numeric := 0; BEGIN FOREACH element IN ARRAY arr LOOP total := total + element; END LOOP; RETURN total; END; $$ LANGUAGE plpgsql;
In this example, the anyarray pseudo type allows us to pass arrays of different data types, such as integer, text, or numeric.
Pseudo types in PostgreSQL provide a powerful mechanism for handling dynamic and generic data types. They allow developers to write more flexible and reusable functions by abstracting away the specific data types. By utilizing these pseudo types effectively, developers can create more efficient and maintainable code.
In summary, pseudo types are useful tools that enhance the versatility and flexibility of PostgreSQL. They allow for the creation of functions and triggers that can handle various data types without needing to define separate versions for each specific case. With their help, developers can write more concise code while maintaining a high level of functionality.